Electrosurgical medical device with power modulation

ABSTRACT

An electrosurgical ablation device provides pulse width modulated DC power to a heating segment in a catheter for use in providing treatment. In some embodiments the DC power to be modulated is sourced from an AC/DC power converter coupled to a source of AC power. In some embodiments the DC power to be modulated is sourced from a battery. In some embodiments the device switchably selects for modulation DC power sourced from either the AC/DC power converter or the battery, for example based on availability of power from the AC/DC power converter.

This application is a continuation of U.S. patent application Ser. No.14/038,827 filed on Sep. 27, 2013, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present embodiments relate generally to medical treatment devices,and more particularly to electrosurgical devices with power modulation.

BACKGROUND OF THE INVENTION

Various medical procedures use a treatment device to apply energy to abody part of a patient. For example, techniques currently used forendovenous treatment for venous reflux disease, as well as otherdiseases in hollow anatomical structures (HAS), include electrosurgicalprocedures, including electrosurgical heating, radio frequency ablation(RFA), and laser ablation. These techniques generally involve atreatment apparatus or system that is configured to heat tissue at atreatment site within the HAS. For example, electrosurgical heating fortreating venous reflux disease may use radio frequency current to applyenergy to create targeted tissue ablation to seal off damaged veins.Electrosurgical equipment typically includes a generator, such as an RFgenerator, and a catheter having a heating segment located at the distalend, which is inserted into the vein(s) during treatment. The heatingsegment may use RF energy driven by the RF generator to heat and sealthe vein. Electrosurgical treatments are also used in other medicaltreatments, such as, for example, arthroscopic surgery, renaldenervation, and cardiac surgery.

Typically, electrosurgical procedures may be performed using devicespowered by alternating current (AC) power sources. Unfortunately, ACpower sources may not always be available or reliable in all locations.

BRIEF SUMMARY OF THE INVENTION

Aspects of the invention relate to electrosurgical devices, for examplefor use in medical treatments capable of utilizing AC and/or DC power,while providing appropriate power to the treatment device to provideeffective and safe treatment. In general, in one aspect, animplementation of the disclosure features a direct current (DC) poweredelectrosurgical device including a catheter having a heating segment andmodulation circuitry configured to modulate DC power provided to theheating segment. The electrosurgical device also includes at least oneDC power source for providing the DC power to the first circuitry.

One or more of the following features maybe included. In some suchaspects the modulation is pulse width modulation (PWM). In some suchaspects the modulation circuitry includes pulse width modulation (PWM)driver circuitry and a switch. In some such aspects the at least one DCpower source comprises two DC power sources. In some such aspects, afirst of the two DC power sources comprises an AC/DC power converter anda second of the two DC power sources comprises a battery. Some suchaspects further comprise a switch to switchably provide power fromeither the AC/DC converter or the battery to the PWM circuitry forprovision to the heating segment. In some such aspects the AC/DCconverter and the battery are coupled in parallel to the PWM circuitry.Some such aspects further comprise a DC/DC power converter coupledbetween the AC/DC power converter and the PWM circuitry. In some suchaspects the heating segment comprises a resistive coil. In some suchaspects the resistive coil is housed in a plastic cover. In some suchaspects a frequency of the PWM is in a range of 1 kHz to 50 kHz,inclusive.

In general, in another aspect, the implementation of the disclosurefeatures a method of operating an electrosurgical device, includingproviding direct current (DC) power, modulating the DC power using pulsewidth modulation (PWM), and applying the modulated DC power to a heatingelement in a catheter.

One or more of the following features maybe included. In some aspectsmodulating the DC power using PWM includes providing the DC power to aswitch, and opening and closing the switch using a PWM driver signal. Insome such aspects a frequency of the PWM is in the range of 1 kHz to 50kHz, inclusive. In some such aspects providing DC power includesselectably providing DC power from an AC/DC power converter or from abattery. In some such aspects selection of provision of DC power fromthe AC/DC power converter or from the battery is based on availabilityof AC power to the AC/DC power converter. In some such aspects selectionof DC power from the AC/DC power converter or from the battery may beperformed during application of power to the heating element.

In general, in still another aspect, the implementation of thedisclosure features an electrosurgical device, including an AC/DC powerconverter and a battery. The device also includes a catheter including aresistive coil. Circuitry is included for switching provision of powerto the resistive coil from power sourced from the AC/DC power converterto power sourced from the battery based on a cessation of availabilityof DC power from the AC/DC power converter.

One or more of the following features maybe included. Some aspectsfurther include pulse width modulation (PWM) circuitry for modulatingpower provided to the resistive coil.

These and other aspects of the invention are more fully comprehendedupon review of this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a medical treatment system in accordance with aspectsof the invention;

FIGS. 1A and 1B are side elevation views of an example procedure usingthe medical treatment system of FIG. 1;

FIG. 2 is a block diagram of an electrosurgical ablation device inaccordance with aspects of the invention;

FIG. 3 is a block diagram of a power block of an electrosurgicalablation device in accordance with aspects of the invention;

FIG. 4 is a set of charts showing pulse width modulation of DC power inaccordance with aspects of the invention;

FIG. 5 is flow diagram of a process for determining adjustments to aduty cycle in accordance with aspects of the invention; and

FIG. 6 is a flow diagram of a process for determining whether to use ACsourced power or battery sourced power in accordance with aspects of theinvention

DETAILED DESCRIPTION

The following discusses various embodiments with reference to thefigures. Directional terms used herein, such as proximal, distal, upper,lower, clockwise, counterclockwise, etc., are generally used withreference to the configurations shown in the figures. For example, acomponent that is described as rotating clockwise when viewed from theperspectives shown in the figures may be said to rotate counterclockwisewhen viewed from the opposite perspective. Furthermore, the presentembodiments may be modified by altering or reversing the positions ordirections of movement of various components. Accordingly, directionalterms used herein should not be interpreted as limiting.

Referring to FIG. 1, an exemplary medical treatment 10 system mayinclude a catheter shaft 12 having a distal end 13 and a proximal end14. A heating segment 15 is operably attached towards or adjacent thedistal end of the catheter shaft and a handle 16 is attached at theproximal end of the catheter shaft. A cable 17 electrically connects theheating segment 15 to a generator system 18. The cable 17 may beintegral to the handle and removably connected to the generator system.Alternatively, the cable 17 may be removably connected to the handle.

The heating segment 15 includes a heating element 20. The heatingelement 20 may in some embodiments be a resistive coil, which may bedriven, for example, by RF energy. Preferably, the relative resistanceor impedance of the heating element 20 is designed to correlate to, ormatch, relative resistance or impedance of an output of the generatorsystem 18 to which the heating element 20 is coupled. For example, theresistance of the heating element 20 may be determined by a wire gagethat relates to the catheter diameter, the energy required duringtreatment, and/or the power source specifications. The heating element20 may comprise a wide variety of conductive materials, such as, forexample, nickel chromium (NICHROME®), a nickel iron alloy (for exampleAlloy 52), copper, stainless steel, titanium, zirconium, NITINOL®,ALUMEL®, KANTHANAL®, CHROMEL®, KOVAR®, combinations or alloys of thesame and the like. The material for the heating element 20 can be chosento provide Resistance Temperature Detector (RTD) functionality, whereintemperature is indirectly measured as a function of impedance. Alloy 52is considered to be one material suitable for providing RTDfunctionality to the resistive coil. In various embodiments theresistive coil may be housed in a plastic cover, for example afluorinated ethylene propylene (FEP) cover.

The heating segment 15 is secured at the distal end 13 of the elongatecatheter shaft 12, with, in some embodiments, the catheter shaft 12 andthe heating segment 15 together being considered a catheter. Thecatheter shaft 12 may be used to maneuver the heating element 20 into adesired placement within a HAS. In certain embodiments, the cathetershaft 12 comprises a biocompatible material having a low coefficient offriction. For example, the catheter shaft 12 may comprise polyetherether ketone (PEEK), polyethylene, or polytetrafluoroethylene (PTFE),such as TEFLON®. In other embodiments, the catheter shaft 12 maycomprise polyimide, thermoplastic elastomer (TPE), such as HYTREL®,polyether block amide (PEBA), such as PEBAX®, nylon, or any other suchsuitable material.

In certain embodiments, the catheter shaft 12 is sized to fit within avascular structure that may be between approximately 1 mm andapproximately 25 mm in diameter and, preferably, between approximately 2mm and approximately 18 mm. The proximal end 14 of the catheter shaft 12includes a handle 16 that may include a connection for interfacing withthe power source 18 through the cable 17, and/or a port for fluid orguidewire passage. The handle 16 may be integrally connected to thecable 17, or the handle 16 may be removably connected to the cable 17.

The exemplary medical treatment system 10 may be used in various medicalprocedures, including endovenous treatments to treat venous reflux.Specifically, referring to FIG. 1A, a method may comprise inserting theheating segment 15 into a distal-most section of a HAS 19 to be treated.The heating segment 15 is then aligned with a first treatment locationTi within the HAS. Power is then applied to the heating segment 15 for adesired length of time to treat the first treatment location T1. After adesired dwell time, such as after the HAS has collapsed as shown in FIG.1B, the power supplied to the heating segment 15 may be reduced or shutoff. With the power off (or substantially reduced), the heating segment15 may then be moved proximally until the distal end of the heatingsegment 15 is adjacent to the proximal end of the first treatmentlocation T1, as shown in FIG. 1B. At this second treatment location T2within the HAS 19, power is again applied to the heating segment 15 fora desired length of time to treat the HAS at the second treatmentlocation T2. This process is repeated until the treatment of the HAS iscomplete. In some embodiments, T1 and T2 may overlap. While T1 and T2are shown adjacent to one another in the same HAS, T1 and T2 may be indifferent locations, such as different HAS.

In certain embodiments, the generator system includes at least onesource of direct current (DC) power and modulation circuitry formodulating that power so that RF energy may be applied to the heatingsegment 15. In most embodiments the RF energy is generated by modulatingDC power applied to the heating segment 15, in some embodiments by pulsewidth modulation (PWM) of the DC power applied to the heating segment15. The modulation circuitry may be, for example, pulse width modulationcircuitry, which in some embodiments comprises pulse width modulationdriver circuitry and a switch. In several embodiments the source of DCpower is coupled to the heating segment 15 by a switch, with the switchopened and closed for various portions of a periodic cycle in accordancewith a pulse width modulation signal. In most embodiments the periodiccycle has a frequency in the radio frequency range, and in someembodiments the periodic cycle has a frequency range between 1 kHz and50 kHz, inclusive. In most embodiments power is applied to the heatingsegment 15 when the switch is closed and not applied when the switch isin the open position, but in some embodiments the converse may be true.In some embodiments the switch may be provided, at least in part, by useof switch used for transfer of power, and in some embodiments the switchmay include a power MOSFET or an insulated-gate bipolar transistor(IGBT). The generator system 18 in various embodiments incorporates acontroller. The controller may be, in various embodiments, one or moreprocessors, FPGAs, CPLDs, DSPs, or some combination thereof. Thecontroller may perform various functions, including determining a dutycycle of the PWM based at least upon readings from a temperature sensoror sensors (e.g., a thermocouple, a thermistor, a resistance temperaturedevice, an optical or infrared sensor, combinations of the same or thelike) located in or adjacent to the heating segment 15. For example, thecontroller may heat the the heating segment 15 to a set temperature. Inan alternative embodiment, the user selects a constant power output ofthe generator system 18. For example, the user may manually adjust thepower output relative to the temperature display from a temperaturesensor in the heating segment 15.

In some embodiments the generator system 18 includes multiple DC powersources, with different ones of the multiple DC power sourcesselectable, for example by the controller commanding operation of powerswitching circuitry, for use in provision of power to the heatingelement 20. For example, in some embodiments the generator system 18 mayinclude, or be provided power from, a battery as one DC power source andan AC/DC power converter coupled to an AC main (utility or generatorpower source), with the controller and power switching circuitryselecting use of one power source or the other based on, for example,availability of power from the AC derived power source. In this context,as shown in FIG. 1, an AC/DC power converter 21, coupled to a housing ofthe generator system 18 by an electrical coupling 23 and coupled to asource of AC power by an electrical coupling 25, may be considered partof the generator system 18. Alternatively, the power converter 21 may beintegral to the generator system 18, such as being a part of theinternal electronics. In some embodiments the controller and powerswitching circuitry may switch the source of power while power isgenerally being provided to the heating element 20, allowing for powersource switching during operation of the medical treatment system 10.

FIG. 2 is a block diagram of an electrosurgical ablation device inaccordance with aspects of the invention. In FIG. 2, an AC/DC powerconverter 211 receives AC power from a power source such as a utility orgenerator. The AC/DC power converter 211 converts the AC power to DCpower. For example, the AC power converter 211 may receive AC power inthe range of 100-240 VA, and output power nominally at 24 V DC, withavailable current for example in the range of a few to several amps.

The DC power is provided, or made available to, a generator unit 213,such as the generator system 18 described above. The generator unit 213provides power to a heating segment (not shown) in FIG. 2 by way ofproviding power to a handle 221 and a catheter 223 coupled to the handle221, with the catheter 223 including the heating segment, for example asdiscussed with respect to FIG. 1, with reference to heating segment 15,handle 16 and catheter shaft 12. In most embodiments the provided poweris pulse width modulated DC power. In many embodiments, and asillustrated in FIG. 2, the generator unit 213 also receives signals fromthe catheter 223, for example signals indicative of temperature of theheating segment. In such embodiment, the generator unit 213 may adjust aduty cycle of the PWM so as to adjust the temperature of the heatingsegment to a desired setting. In many embodiments the PWM has a periodiccycle in the RF range, and in some embodiments has a periodic cycle inthe range of 1 kHz to 50 kHz, inclusive.

The generator unit 213 includes a power block 215 and, in the embodimentillustrated in FIG. 2, a control block 217 and a monitor block 219.

The power block 215 receives DC power sourced from the AC/DC powerconverter 211. The power block 215 provides power to the handle 221 andthe catheter 223 coupled to the handle 221. The catheter 223 includes aheating segment (not shown), for example as discussed with respect toFIG. 1. The power block 215 therefore effectively provides power to theheating segment. In providing power to the heating segment, the powerblock 215 modulates DC power to provide modulated RF power to theheating segment, for example using modulation circuitry of the powerblock 215. In most embodiments the modulation is pulse width modulation(PWM), and the modulation circuitry may be pulse width modulationcircuitry, for example including pulse width modulation driver circuitryand a switch. In various embodiments duty cycle of the PWM is determinedby the control block 217, for example based on a desired temperature ofthe heating segment and signals from the catheter 223 indicative oftemperature of the heating segment. In some embodiments the DC powerwhich is modulated is at a different voltage than that provided by theAC/DC power converter 211, and in such embodiments one or more DC/DCpower converters may be utilized to provide the DC power which ismodulated. In some embodiments the AC/DC converter 211 provides DC powerat 24 Volts, and the DC power which is modulated is about 15 Volts, forexample 15 Volts to 16.8 Volts or 15.5 Volts.

The power block 215 also provides power signals, and in some embodimentsstatus signals, to a control block 217 and the monitor block 219. Thepower signals provided to the control block 217 and the monitor block219 are in some embodiments appropriate for powering of circuitry withinthose blocks, and in other embodiments are appropriate for use by powercontrol circuitry within those other blocks in powering circuitry, forexample CMOS circuitry. The status signals may provide various signalsrelating to the status of power available to the power block 215.

In some embodiments the power block 215 also includes a battery 225 and,in some such embodiments, a battery charger. The battery 225 may be inthe form of a battery pack. In various embodiments the battery 225 maybe physically separate from the power block 215, and in some embodimentsmay be external to a housing of the generator unit 213. In someembodiments the battery 225 may be for example a Lithium-ion batterypack. A Lithium-ion battery may be rechargeable, and in embodiments inwhich rechargeable batteries are used, the power block 215 may includebattery charging circuitry. The battery charging circuitry may beprovided power from the AC/DC power converter 211 in some embodiments,or a DC/DC power converter as previously discussed.

In embodiments in which the power block 215 includes a battery 225, thepower block 215 may select, for example, using power switching circuitryof the power block 215, one or the other of DC power sourced from theAC/DC power converter 211 or DC power sourced from the battery 225 formodulation and provision to the heating segment of the catheter 223. Insome embodiments the power block 215 may utilize DC power sourced fromthe AC/DC power converter 211 if such DC power is available, and utilizeDC power sourced from the battery 225 if DC power is not available fromthe AC/DC power converter 211. Similarly, power signals to the controlblock 217 and monitor block 219 also may be selected from either theAC/DC power converter 211 or the battery 225. In some embodiments statusof availability of power from the AC/DC power converter 211 is providedto the control block 217, and the control block 217 provides commandsignals to the power block 215 instructing the power block 217 as towhich source of power to utilize.

As indicated above, the control block 217 may receive signals indicativeof temperature of the heating segment from the catheter 223 (by way ofthe handle 221) and signals indicative of availability of power sourcedfrom the AC/DC power converter 211. Based on these signals, and invarious embodiments other signals, the control block 217 may determine aduty cycle for pulse width modulation of the DC power to be provided tothe catheter 223 and selection of a source of power to provide that DCpower. Results of those determinations may be provided to the powerblock 215 in the form of command signals to the power block 215. In someembodiments the command signals include a signal indicating a duty cyclefor PWM of the DC power. In some embodiments the control block 217includes a programmable processor to make those determinations. Thecontrol block 217 may be implemented using a microcontroller andassociated circuitry in various embodiments. In some embodiments thecontrol block 217 also includes power regulation circuitry forregulating power provided by the power block 215 for operation ofcircuitry of the control block 217. In various embodiments the controlblock 217 also receives signals indicative of user inputs to thegenerator unit 213, and provides commands for display of indicators, forexample LED indicators, of the generator unit 213.

The monitor block 219 also receives signals indicative of temperatureabout the heating segment from the catheter 223 (by way of the handle221), as well as power and status signals from the power block 215. Themonitor block 219 may include circuitry for performing variousmonitoring functions related to the status of the generator unit 213 andcatheter 223.

FIG. 3 is a block diagram of a power block 300 in accordance withaspects of the invention. In some embodiments the power block 300 ofFIG. 3 is the power block 215 of FIG. 2, and in some embodiments thepower block 300 of FIG. 3 is similar to the power block 215 of FIG. 2.In various embodiments the power block 300 of FIG. 3 is a portion of thepower block 215 of FIG. 2, and in some embodiments the power block 300of FIG. 3 includes circuitry found in other blocks of the system of FIG.2.

The power block 300 of FIG. 3 includes an AC/DC power converter 311. Invarious embodiments, however, the AC/DC power converter 311 is externalto the power block 300. The AC/DC power converter 311 is coupled to asource of AC power, for example a utility main or a generator, and theAC/DC power converter 311 converts AC power to DC power.

The DC power supplied by the AC/DC power converter 311 is provided to aDC/DC power converter 313. In most embodiments the DC/DC power converter313 converts the DC power supplied by the AC/DC power converter 311 to adifferent power level. For example, the AC/DC power converter 311 mayprovide DC power at 24 Volts DC and the DC/DC power converter 313 mayconvert the power to 15.5 Volts DC. In some embodiments additional DC/DCpower converters may be included between the AC/DC power converter 311and the DC/DC power converter 313, for example to provide for electricalisolation features in event of voltage spikes from external sources. DCpower from the DC/DC power converter 313 is provided to a pulse widthmodulator 323, for provision of pulse width modulated power to a heatingsegment of a catheter.

The pulse width modulator 323, which in some embodiments comprises aswitch, modulates the DC power to provide modulated DC power for use bya heating segment of a catheter, for example heating segment 15 ofFIG. 1. The pulse width modulator 323 modulates the DC power inaccordance with signals from a PWM driver 325, and in some embodimentsthe PWM driver comprises PWM driver circuitry, with the PWM drivercircuitry and the switch together comprising PWM modulation circuitry.In some embodiments the PWM driver 325 is external to the power block.The PWM driver 325 provides signals to the pulse width modulator 323commanding the pulse width modulator 323 to turn on and off output powerover various portions of a cycle. In some embodiments the cycle is at afrequency in the range of 1 kHz to 50 kHz, inclusive. In manyembodiments the PWM driver 325 provides the signals driving operation ofthe pulse width modulator 323 based on a command signal, for exampleprovided by a control block, for example the control block 217 of FIG.2, indicating a desired duty cycle for pulse width modulation.

For illustrative purposes, FIG. 4 includes charts illustrating exampleon and off portions of a cycle for various duty cycles. In the charts,time is shown along an x-axis and output voltage is shown along ay-axis. The charts show idealized output voltages, as for example inmost embodiments rises and falls in output voltage will take placeduring discrete periods of time. A first chart 411 illustrates a 25%duty cycle, with a high output voltage during a time period 413, a lowoutput voltage during a time period 415, with a return to the highoutput voltage at an end 417 of the time period 415. The time periods413 and 415 form a complete cycle, with the time period 413 being 25% ofthe cycle and the time period 415 being 75% of the cycle. A second chart421 illustrates a 50% duty cycle, with a high output voltage during atime period 423, a low output voltage during a time period 425, with areturn to the high output voltage at an end 427 of the time period 425.The time periods 423 and 425 form a complete cycle, with the time period423 and the time period 425 each being 50% of the cycle. A third chart431 illustrates a 75% duty cycle, with a high output voltage during atime period 433, a low output voltage during a time period 435, with areturn to the high output voltage at an end 437 of the time period 435.The time periods 433 and 435 form a complete cycle, with the time period433 being 75% of the cycle and the time period 435 being 25% of thecycle.

Returning to FIG. 3, in some embodiments, and as illustrated in FIG. 3,either AC sourced power or battery sourced power may be used to provideDC power for modulation. Accordingly, in the embodiment of FIG. 3 thepower block 300 includes a battery 317. In various embodiments, thebattery 317 may be separate from the power block 300. The battery 317also may provide DC power to the pulse width modulator 323, with a firstpower switch 321 selectably choosing either the AC sourced powerprovided by the DC/DC converter 313 or DC power for modulation by thepulse width modulator 323. In some embodiments the first power switch321 selects the AC sourced power or the battery power based on a controlsignal provided by a control block, for example control block 217 asdiscussed with respect to FIG. 2. In some embodiments the first powerswitch 321 is not used, with an output of the battery 317 and an outputof the DC/DC power converter 313 connected in parallel, with both theDC/DC power converter 313 output and the battery 317 output presenting ahigh impedance.

In embodiments with a battery 317, the power block 300 may also includea battery charger module 315. As with the battery 317 in variousembodiments, the battery charger module 315 may be external to the powerblock. The battery charger module 315 includes battery chargingcircuitry for charging the battery 317 using power from the AC/DCconverter 311.

As shown in FIG. 3, the AC/DC power converter 311 and the battery 317are also coupled to a second power switch 319. The second power switch319 provides power for use by various circuit elements, for examplecircuitry of the control block 217 and monitor block 219 of thegenerator unit 213 of FIG. 2.

FIG. 5 is a flow diagram of a process for determining adjustments to aduty cycle in accordance with aspects of the invention. In someembodiments the process is performed by circuitry, which may be in theform of a processor. In some embodiments the process is performed by thecontrol block 217 of FIG. 2, and in some embodiments the process isperformed by a programmable processor of the control block 217 of FIG.2.

In block 511 the process compares actual temperature of a heatingsegment of a catheter, or temperature about a heating segment of acatheter, with a desired temperature. The temperature about the heatingsegment of the catheter may be provided by a temperature sensor locatedin the catheter near the heating segment, for example. The desiredtemperature may be a constant temperature in some embodiments. In someembodiments the desired temperature may be enterable by a user into, forexample, the generator unit 213 of FIG. 2, with an entered temperaturereceived by the control block 217 of FIG. 2.

In block 513 the process determines if the actual temperature is greaterthan the desired temperature plus a first offset value. The use of anoffset value, which may be programmable in various embodiments, may beuseful in avoiding, for example, excessive frequency of changes in theduty cycle, while generally maintaining the actual temperature in adesired temperature band. If the actual temperature is greater than thedesired temperature plus the offset value, the process continues toblock 515, otherwise the process continues to block 517.

In block 515 the process decreases the duty cycle. In some embodimentsthe process decreases the duty cycle by a set amount, down to a minimum,which is greater than 0% in some embodiments. The process thereafterreturns.

In block 517 the process determines if the actual temperature is lessthan the desired temperature minus a second offset value. The secondoffset value is in some embodiments the same as the first offset value.In some embodiments the second offset value is greater than the firstoffset value, and in some embodiments the second offset value is lessthan the first offset value. If the actual temperature is less than thedesired temperature minus the offset value, the process continues toblock 519, otherwise the process returns.

In block 519 the process increases the duty cycle. In some embodimentsthe process increases the duty cycle by a set amount, up to a maximum,which is less than 100% in some embodiments. The process thereafterreturns.

FIG. 6 is a flow diagram of a process for determining whether to use ACsourced power or battery sourced power in accordance with aspects of theinvention. In some embodiments the process is performed by circuitry,which may be in the form of a processor. In some embodiments the processis performed by the control block 217 of FIG. 2, and in some embodimentsthe process is performed by a programmable processor of the controlblock 217 of FIG. 2. In some embodiments the process is performed beforepower is applied to a heating segment of a catheter. In some embodimentsthe process is performed while power is applied to the heating segment.In some embodiments the process is performed both before power isapplied to the heating segment and while power is applied to the heatingsegment.

In block 611 the process determines if AC sourced power is available.The process may determine whether AC sourced power is available based ona signal provided by, for example, the power block 215 of the generatorunit 213 of FIG. 2. If AC sourced power is available the processcontinues to block 613, otherwise the process continues to block 615.

In block 613 the process uses AC sourced power to supply DC power to bemodulated for provision to the heating segment of the catheter. Invarious embodiments the process also utilizes AC sourced power, withgenerally the AC sourced power converted to DC by for example an AC/DCpower converter, for powering of circuitry and, in some embodiments, forcharging of the battery. The process thereafter returns.

In block 615 the process uses battery sourced power to supply DC powerto be modulated for provision to the heating segment of the catheter. Invarious embodiments the process also utilizes the battery sourced powerfor powering of circuitry, and in some embodiments commands ceasing ofcharging of the battery. The process thereafter returns.

Although the invention has been discussed with respect to variousembodiments, it should be recognized that the invention comprises thenovel and non-obvious claims supported by this disclosure.

1-19. (canceled)
 20. A medical system comprising: a heating elementconfigured to ablate tissue; a power converter configured to convert ahigh direct current (DC) power to a low DC power lower than the high DCpower; a pulse width modulator configured to modulate the second DCpower and deliver DC power pulses to the heating element; and a pulsewidth modulation (PWM) driver configured to provide signals that controlthe pulse width modulator to turn on and off power to generate the DCpower pulses.
 21. The medical system of claim 20, further comprising acatheter including a heating segment comprising the heating element. 22.The medical system of claim 20, wherein the DC power pulses comprise aminimum duty cycle greater than 0% and a maximum duty cycle less than100%.
 23. The medical system of claim 22, wherein the PWM driver isconfigured to control the pulse width modulator to decrease a duty cycleof the DC power pulses in response to a sensed temperature from atemperature sensor being greater than a desired temperature plus a firstoffset value, and wherein the PWM driver is configured to control thepulse width modulator to increase the duty cycle of the DC power pulsesin response to the sensed temperature from the temperature sensor beingless than the desired temperature minus a second offset value.
 24. Themedical system of claim 20, further comprising an AC/DC power converterand a battery.
 25. The medical system of claim 24, further comprising aswitch configured to switchably provide power from either the AC/DCconverter or the battery to the pulse width modulator.
 26. The medicalsystem of claim 25, wherein the AC/DC converter and the battery arecoupled in parallel to the switch.
 27. The medical system of claim 25,wherein the power converter is coupled between the AC/DC power converterand the switch.
 28. The medical system of claim 20, wherein the heatingelement is a resistive coil.
 29. The medical system of claim 20, whereinthe heating element is constructed of at least one of nickel chromium, anickel iron alloy, copper, stainless steel, titanium, or zirconium. 30.The medical system of claim 20, wherein the heating element isconstructed of a material from which temperature is indirectly measuredas a function of impedance, and wherein the medical system comprises atemperature sensor configured to measure the temperature as the functionof the impedance of the heating element.
 31. The medical system of claim20, further comprising plastic cover within which the heating element ishoused.
 32. A method comprising: converting, by a power converter of amedical system, a high direct current (DC) power to a low DC power lowerthan the high DC power; modulating, by a pulse width modulator of themedical system, the low DC power; delivering, by the pulse widthmodulator, DC power pulses to a heating element; and providing, by apulse width modulation (PWM) driver of the medical system, signalscontrolling the pulse width modulator to turn on and off power togenerate the DC power pulses.
 33. The method of claim 32, wherein themedical system comprises a catheter including a heating segmentcomprising the heating element.
 34. The method of claim 32, wherein theDC power pulses comprise a minimum duty cycle greater than 0% and amaximum duty cycle less than 100%.
 35. The method of claim 34, furthercomprising: controlling, by the PWM driver, the pulse width modulator todecrease a duty cycle of the DC power pulses in response to a sensedtemperature from a temperature sensor being greater than a desiredtemperature plus a first offset value; and controlling, by the PWMdriver, the pulse width modulator to increase the duty cycle of the DCpower pulses in response to the sensed temperature from the temperaturesensor being less than the desired temperature minus a second offsetvalue.
 36. The method of claim 32, further comprising switchablyproviding, by a switch, power from either an AC/DC converter or abattery to the pulse width modulator, wherein the AC/DC converter andthe battery are coupled in parallel to the switch.
 37. The method ofclaim 32, further comprising switchably providing, by a switch, powerfrom either an AC/DC converter or a battery to the pulse widthmodulator, wherein the power converter is coupled between the AC/DCpower converter and the switch.
 38. The method of claim 32, wherein theheating element is constructed of a material from which temperature isindirectly measured as a function of impedance, and wherein the methodfurther comprises measuring, by a temperature sensor, the temperature asthe function of the impedance of the heating element.
 39. A medicalsystem comprising: a heating element configured to ablate tissue; anAC/DC power converter; a battery; a power converter configured toconvert a high direct current (DC) power to a low DC power lower thanthe high DC power; a pulse width modulator configured to modulate thesecond DC power and deliver DC power pulses to the heating element; aswitch configured to switchably provide power from either the AC/DCconverter or the battery to the pulse width modulator; and a pulse widthmodulation (PWM) driver configured to provide signals that control thepulse width modulator to turn on and off power to generate the DC powerpulses, wherein the PWM driver is configured to control the pulse widthmodulator to decrease a duty cycle of the DC power pulses in response toa sensed temperature from a temperature sensor being greater than adesired temperature plus a first offset value, and wherein the PWMdriver is configured to control the pulse width modulator to increasethe duty cycle of the DC power pulses in response to the sensedtemperature from the temperature sensor being less than the desiredtemperature minus a second offset value.